Crossbow
The Crossbow is a long awaited weapon for the Assassin's Creed series. This weapon was originally seen in the trailer for Assassin's Creed, but was not included in the game due to historical inaccuracies.
The crossbow has been confirmed as a weapon in Assassin's Creed: Brotherhood. After being spotted in a concept art, and being mentioned in the E3 2010 Single-Player walkthrough, Jean francois boivin stated that long ranged weapons such as the crossbow will be available for advanced horse combat.
Since it is a weapon that requires ammo, arrows and bolts are suspected to be purchasable at the Blacksmith. It is unknown what the maximum amount of ammo for the Crossbow or if the amount could be maximized, possibly by upgrading pouches at the Tailor, like in Assassin's creed II.